Effects of Electronegative Substituents of Anions on Ion-Pair Formation. 2. The Temperature Dependence of Conductivity of Lithium Trifluoroacetate and Lithium Difluoroacetate Solutions in Propylene Carbonate

Abstract

The interpretation of the molar conductivity of lithium trifluoroacetate and lithium difluoroacetate solutions in propylene carbonate obtained from precise measurements at temperatures 238.15 ≤ T/K ≤ 308.15 in the concentration range 7 < 104 c/mol dm-3 < 90 requires the consideration of ion-pair and unilateral triple-ion formation despite the high permittivity of the solvent. Association constants and triple-anion formation constants strongly increase at decreasing temperature, in accordance with the assumption of strong non-Coulombic effects. At all temperatures the association constants of lithium trifluoroacetate are lower than those of lithium difluoroacetate, revealing the electron withdrawing effect of the substituent decreasing the charge density on the oxygen atoms. Traces of water increase the conductivity of the solution, showing that water selectively solvates the lithium ion.